Femtocell network system is designed to provide the wireless communication users with voice and data transmission services of high data rate at low prices. Femto access point (FAP) is a tiny communication base station which provides small service coverage in the indoor environment. Each FAP can be configured as open or closed according to the access authority. The open FAP is configured to allow access from all user equipments (UEs), such as, mobile devices. The closed FAP is configured to allow specific UEs to access, and other UEs without access rights to the FAP are called “inadmissible visiting UEs”.
A universal mobile telecommunication system (UMTS) base station (Node B) is a wide area base station which has bigger service coverage than a FAP does. That is, a UMTS base station/Node B may enclose a number of areas served by FAPs. As an inadmissible visiting UE approaches a closed FAP, the signals from the FAP received by the UE may be stronger than that from the UMTS Node B. When the signals from FAP are so strong to overwhelm the signals from UMTS Node B that an inadmissible visiting UE can only receive the signals from the FAP, the inadmissible visiting UE will not be able to access the UMTS Node B. Meanwhile, the closed FAP rejects the access of the inadmissible visiting UE, such that the connection of the UE is thoroughly lost and the communication is interrupted. After the Femtocell network system is deployed, the above-mentioned scenarios will eventually pose the deadzone effect to the inadmissible visiting UEs in the communication environment.
In other words, for inadmissible visiting UEs that are too close to a closed FAP, the UEs can only receive the signals and messages from the closed FAP to which the UEs have no right to access, will lead to a communication deadzone.
FIG. 1 shows a schematic view of the deadzone effect of Femtocell network system. In the upper part of FIG. 1, the y-axis is the received signal code power (RSCP), and the x-axis is the distance between an inadmissible visiting UE (marked as 101) and a FAP (marked as 102). Lines 110 and 120 represent the UE measured RSCPs of FAP and UMTS Node B, respectively. The closer UE 101 approaches to the FAP, the stronger the RSCP of FAP is. In the lower part of FIG. 1, area A1 is referred to as the FAP coverage, where the RSCP of the common pilot channel (CPICH) of FAP is greater than or equal to that of the UMTS Node B. Area A2 is referred to as the FAP dominance, where the CPICH RSCP of the FAP surpasses the CPICH RSCP of UMTS Node B so that UEs in this area are required to perform location update or handoff process to the FAP. Area A3 is referred to as FAP deadzone, which is the area where the FAP signal overwhelms the signal of UMTS Node B that UEs in this area can only detect and receive signals and messages from the FAP.
The UE in area A1 may simultaneously receive signals and messages from the FAP and UMTS Node B. The UE in area A2 may also receive signals and messages from UMTS Node B at the same time, but the signal strength and the quality from FAP dominates those from the UMTS Node B. The UE in area A3 cannot detect or receive any signals from UMTS Node B.
Prior to the present disclosure, two methods are already known in order to handle the Femtocell deadzone effect. The first one is, when the UE enters the deadzone caused by the deployment of a closed FAP, the UE searches for the Global System for Mobile Communications (GSM) base station and performs handoff process to the GSM system to keep the communication. The drawback of this solution is, the UE which handoffs to the GSM system may not be able to access to the services that require high bandwidth as it was in UMTS. The second one is to allocate a different frequency band to Femtocell network system so that UEs in UMTS network shall have less interference from closed FAP. In this manner, the extent of Femtocell deadzone can be greatly decreased. However, this can not entirely eliminate the existence of Femtocell deadzone. In addition, this method will incur an additional cost of using specific 3G frequency band for the Femtocell network operator.
U.S. Patent Publication No. 2007/0097939 disclosed an automatic configuration technique for femto radio base station (Femto Access Point, FAP), proposing that through communication with FAP, macrocell (the UMTS network) may collect the signal quality-related parameters in the FAP coverage and generate parameters related to the FAP transmission power configuration, therefore, minimizing the impact of FAP on macrocell.